Semen is the cloudy white bodily fluid that is emitted from the urethra and out of the penis during ejaculation. It consists of mobile sperm cells (called spermatozoa) and a nutrient-rich fluid called seminal fluid. The purpose of the seminal fluid is to both transport the sperm cells and enhance their fertilization abilities.

How Is Semen Produced?

Sperm cells are produced in the testes, stored in the epididymis, and comprise less than 10 percent of semen—a tidbit that may surprise you. During ejaculation, a thick-walled duct called the vas deferens carries the sperm cells from the epididymis to the urethra and then outside of the body or into the vagina by means of the penis.

As the sperm cells travel through the vas deferens, three different glands release mucous secretions (called the seminal fluid) that combine with the sperm cells to create semen. These three glands, often referred to as accessory sex glands, are the bulbourethral glands (also called Cowper's glands), the prostate gland, and the seminal vesicles.

Cowper's Glands

The first portion of seminal fluid (about 5 percent) consists of secretions from the Cowper's glands. These pea-sized glands produce what is called the pre-ejaculate fluid, the small amount of fluid that is released before ejaculation. This fluid lubricates the urethra and neutralizes any acidity, allowing the sperm to travel easily.

Prostate Gland

Around 15 percent to 30 percent of semen is produced by the prostate gland, a walnut-sized gland located at the base of the bladder surrounding a man's urethra. The prostate gland is the primary source of acid phosphatase, citric acid, inositol, calcium, zinc, and magnesium. All of these unique components play a role. For example, zinc is believed to be an antibacterial factor. Interestingly, some experts believe that this may contribute to the reason why urinary tract infections are not as common in men compared to women.

The prostate gland also releases enzymes that work to liquefy semen about 15 to 30 minutes after ejaculation. This liquefying process allows the sperm to be slowly released. The sperm cells can then enter the cervix and travel upstream in the female reproductive system in an orderly fashion, with the ultimate goal of finding an egg to fertilize.
Seminal Vesicles (Seminal Glands)

Around 65 percent to 75 percent of seminal fluid is produced by the seminal vesicles, which are located above the prostate gland at the base of the bladder. They contribute components like fructose (a sugar) and prostaglandins. Fructose nourishes the sperm cells, providing them with energy. Prostaglandins help trigger contraction of vaginal muscles in order to propel the sperm up the vaginal canal and through the cervix.

Clotting factors are also present in the fluid secreted by the seminal vesicles. This makes the semen clump together, forming a jelly-like consistency right after ejaculation. The purpose of the clotting process is to hold the sperm in place until they can be slowly released during the liquefying process (controlled by enzymes secreted by the prostate gland).

Here are some answers to common questions about semen.

What Does Semen Smell and Taste Like?

Semen often has a chlorine-like smell and tastes slightly sweet due to its high content of fructose. That being said, the taste of semen tends to change slightly from person to person and may be affected by diet.

What is the Normal Volume of Semen Released During Ejaculation?

The volume of semen that is released during ejaculation varies among research studies, although a review study in the Journal of Andrology suggests that the average volume is around 3.4 ml. Also, two factors that may affect semen volume during ejaculation include the last time you ejaculated and hydration status.

What May Red or Brown Semen Indicate?

If your semen has a red or brown appearance, it can be a sign of blood. While this may seem alarming to you, in most instances, blood in your semen (called hematospermia) is usually benign. The most common reason for it is from a prostate biopsy, but it can also be due to a variety of other conditions that affect the organs of the male reproductive tract like an infection. Rarely, blood in the semen is a sign of cancer.

The good news is that hematospermia generally resolves on its own. However, it's important to get it checked out by your doctor. He will likely ask you questions, perform an examination (especially of the scrotum and prostate gland), and do a urine test to make sure an infection is not the cause.

What May Yellow or Green Semen Indicate?

Normal semen may have an off-white or slightly yellow tint. But, semen with a pronounced yellow or green color may indicate an infection like the sexually transmitted infection (STI) gonorrhea. If your semen is discolored due to a gonorrhea infection, treatment with antibiotics prescribed by a doctor will be necessary. Likewise, if your semen is foul-smelling, go and see your doctor as this is also often a sign of infection.

Your semen is not as simple as you may have thought. It has lots of components to it, all of which play a role in enhancing reproduction—your sperm reaching an ovulated egg. However, it's important to note that the fluid part is not absolutely critical for fertilization, as evidenced by intracytoplasmic sperm injection in which a single sperm is injected into an egg.

Of course, if you have any questions or concerns about your semen, please contact your doctor – and don't be embarrassed, this is what they are trained to do.

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